Working fluid for heat cycle, composition for heat cycle system, and heat cycle system

ABSTRACT

A working fluid for heat cycle, a composition for a heat cycle system containing the working fluid, and a heat cycle system employing the composition are provided. The working fluid has a low global warming potential and can replace R410A. The working fluid contains trifluoroethylene, 2,3,3,3-tetrafluoropropene, and optionally a hydrofluoroolefin other than trifluoroethylene and 2,3,3,3-tetrafluoropropene. The total proportion of trifluoroethylene and 2,3,3,3-tetrafluoropropene based on the entire amount of the working fluid is from 70 to 100 mass %.

TECHNICAL FIELD

The present invention relates to a working fluid for heat cycle, acomposition for a heat cycle system comprising the working fluid, and aheat cycle system employing the composition.

BACKGROUND ART

In this specification, abbreviated names of halogenated hydrocarboncompounds are described in brackets after the compound names, and inthis specification, the abbreviated names are employed instead of thecompound names as the case requires.

Heretofore, as a working fluid for heat cycle such as a refrigerant fora refrigerator, a refrigerant for an air-conditioning apparatus, aworking fluid for power generation system (such as exhaust heat recoverypower generation), a working fluid for a latent heat transport apparatus(such as a heat pipe) or a secondary cooling fluid, a chlorofluorocarbon(CFC), such as chlorotrifluoromethane or dichlorodifluoromethane or ahydrochlorofluorocarbon (HCFC) such as chlorodifluoromethane has beenused. However, influences of CFCs and HCFCs over the ozone layer in thestratosphere have been pointed out, and their use is regulated atpresent.

Under the above conditions, as a working fluid for heat cycle, ahydrofluorocarbon (HFC) which has less influence over the ozone layer,such as difluoromethane (HFC-32), tetrafluoroethane or pentafluoroethane(HFC-125) has been used, instead of CFCs and HCFCs. For example, R410A(a pseudoazeotropic mixture refrigerant of HFC-32 and HFC-125 in a massratio of 1:1) is a refrigerant which has been widely used. However, itis pointed out that HFCs may cause global warming.

R410A has been widely used for a common air-conditioning apparatus suchas a so-called package air-conditioner or room air-conditioner, due toits high refrigerating capacity. However, it has a global warmingpotential (GWP) of so high as 2,088, and accordingly development of aworking fluid with low GWP has been desired. Further, development of aworking fluid has been desired on the condition that R410A is simplyreplaced and existing apparatus will be used as they are.

Accordingly, in recent years, a hydrofluoroolefin (HFO) i.e. a HFChaving a carbon-carbon double bond is expected, which is a working fluidhaving less influence over the ozone layer and having less influenceover global warming, since the carbon-carbon double bond is likely to bedecomposed by OH radicals in the air. In this specification, a saturatedHFC will be referred to as a HFC and distinguished from a HFO unlessotherwise specified. Further, a HFC may be referred to as a saturatedhydrofluorocarbon in some cases.

2,3,3,3-Tetrafluoropropene (HFO-1234yf) is known as a working fluidhaving a low global warming potential (GWP). However, althoughHFO-1234yf has a high coefficient of performance, its refrigeratingcapacity is low as compared with R410A, and it cannot be used forconventional air-conditioning apparatus, etc., for which R410A has beenused, such as a so-called package air-conditioner and roomair-conditioner.

As a working fluid employing a HFO, for example, Patent Document 1discloses a technique relating to a working fluid usingtrifluoroethylene (HFO-1123) which has the above properties and withwhich excellent cycle performance will be obtained. Patent Document 1also discloses an attempt to obtain a working fluid comprising HFO-1123and various HFCs in combination for the purpose of increasing the flameretardancy, cycle performance, etc. of the working fluid.

It has been know that HFO-1134yf is useful as a HFO to be used for aworking fluid for heat cycle, and a technique relating to HFO-1234yf hasbeen developed. For example, Patent Document 2 discloses compositionscontaining HFO-1234yf obtainable in production of HFO-1234yf by aspecific process. The compositions disclosed in Patent Document 2contain many compounds, and compositions containing HFO-1234yf andHFO-1123 are included. However, HFO-1123 is disclosed only as aby-product of HFO-1234yf together with many other compounds, and PatentDocument 2 failed to disclose use of a composition containing the two ina specific proportion as a working fluid and that the composition hasexcellent coefficient of performance and refrigerating capacity.

Heretofore, a combination of HFO-1234yf and HFO-1123 has not been foundor indicated in any documents yet, with a view to obtaining a workingfluid which is practically useful comprehensively considering thebalance of the capacity, the efficiency and the temperature gradient asan alternative to R410A.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: WO2012/157764

Patent Document 2: JP-A-2012-505296

DISCLOSURE OF INVENTION Technical Problem

The present inventor has confirmed that the critical temperature ofHFO-1123 is 59.2° C. Thus, it was found that as an alternative toconventionally used R410A, HFO-1123 has a low critical temperature andit can substitute working fluids only in a limited range. Further, evenwhen various HFCs disclosed in Patent Document 1 are combined,sufficient coefficient of performance and refrigerating capacity cannotnecessarily be achieved. The object of the present invention is toprovide a working fluid for heat cycle which achieves not only thecritical temperature but also sufficient cycle performance as analternative to R410A simultaneously, a composition for a heat cyclesystem comprising the working fluid, and a heat cycle system employingthe composition.

Further, the object of the present invention is to provide a workingfluid for heat cycle with which practically sufficient cycle performancewill be obtained while suppressing the influence over global warming, acomposition for a heat cycle system comprising the working fluid, and aheat cycle system employing the composition.

Solution to Problem

Under these circumstances, the present inventor has accomplished thepresent invention by intentionally using HFO-1234yf having a lowrefrigerating capacity in combination with HFO-1123 in a specificproportion.

That is, the present invention provides a working fluid for heat cycle,a composition for a heat cycle system and a heat cycle system of thefollowing [1] to [15].

[1] A working fluid for heat cycle, which contains trifluoroethylene and2,3,3,3-tetrafluoropropene, wherein the total proportion oftrifluoroethylene and 2,3,3,3-tetrafluoropropene based on the entireamount of the working fluid is from 70 to 100 mass %, and the proportionof trifluoroethylene based on the total amount of trifluoroethylene and2,3,3,3-tetrafluoropropene is from 35 to 95 mass %.[2] The working fluid for heat cycle according to [1], wherein the totalproportion of trifluoroethylene and 2,3,3,3-tetrafluoropropene based onthe entire amount of the working fluid is from 80 to 100 mass %.[3] The working fluid for heat cycle according to [1] or [2], whereinthe proportion of trifluoroethylene based on the total amount oftrifluoroethylene and 2,3,3,3-tetrafluoropropene is from 40 to 95 mass%.[4] The working fluid for heat cycle according to any one of [1] to [3],wherein the proportion of trifluoroethylene based on the entire amountof the working fluid is at most 70 mol %.[5] The working fluid for heat cycle according to any one of [1] to [4],which further contains a saturated hydrofluorocarbon.[6] The working fluid for heat cycle according to any one of [1] to [5],which further contains a hydrofluorocarbon having a carbon-carbon doublebond other than trifluoroethylene and 2,3,3,3-tetrafluoropropene.[7] The working fluid for heat cycle according to [6], wherein thehydrofluorocarbon having a carbon-carbon double bond is at least onemember selected from the group consisting of 1,2-difluoroethylene,2-fluoropropene, 1,1,2-trifluoropropene,trans-1,2,3,3,3-pentafluoropropene, cis-1,2,3,3,3-pentafluoropropene,trans-1,3,3,3-tetrafluoropropene, cis-1,3,3,3-tetrafluoropropene and3,3,3-trifluoropropene.[8] The working fluid for heat cycle according to [6] or [7], whereinthe hydrofluorocarbon having a carbon-carbon double bond istrans-1,3,3,3-tetrafluoropropene.[9] The working fluid for heat cycle according to [5], wherein thesaturated hydrofluorocarbon is at least one member selected from thegroup consisting of difluoromethane, 1,1-difluoroethane,1,1,1-trifluoroethane, 1,1,2,2-tetrafluoroethane,1,1,1,2-tetrafluoroethane and pentafluoroethane.[10] The working fluid for heat cycle according to [5] or [9], whereinthe saturated hydrofluorocarbon is at least one member selected from thegroup consisting of difluoromethane, 1,1,1,2-tetrafluoroethane andpentafluoroethane.[11] The working fluid for heat cycle according to [10], wherein thesaturated hydrofluorocarbon is difluoromethane, and based on the totalamount of trifluoroethylene, 2,3,3,3-tetrafluoropropene anddifluoromethane, the proportion of trifluoroethylene is from 30 to 70mass %, the proportion of 2,3,3,3-tetrafluoropropene is at most 40 mass%, and the proportion of difluoromethane is at most 30 mass %, and theproportion of trifluoroethylene based on the entire amount of theworking fluid is at most 70 mol %.[12] A composition for a heat cycle system, which comprises the workingfluid for heat cycle as defined in any one of [1] to [11] and alubricating oil.[13] A heat cycle system, which employs the composition for a heat cyclesystem as defined in [12].[14] The heat cycle system according to [13], which is a refrigeratingapparatus, an air-conditioning apparatus, a power generation system, aheat transport apparatus or a secondary cooling machine.[15] The heat cycle system according to [13], which is a roomair-conditioner, a store package air-conditioner, a building packageair-conditioner, a plant package air-conditioner, a gas engine heatpump, a train air-conditioning system, an automobile air-conditioningsystem, a built-in showcase, a separate showcase, an industrial fridgefreezer, an ice making machine or a vending machine.

Advantageous Effects of Invention

The working fluid for heat cycle and the composition for a heat cyclesystem containing the working fluid of the present invention have lessinfluence over global warming and have practically sufficient heat cycleperformance.

The heat cycle system of the present invention, which employs thecomposition for a heat cycle system of the present invention, has lessinfluence over global warming and has practically sufficient heat cycleperformance.

Further, the working fluid for heat cycle of the present inventionsatisfies the above conditions and can replace conventionally usedR410A.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a composition range of a working fluidfor heat cycle of the present invention in triangular coordinates of acomposition (mass %) of a mixture of HFO-1123, HFO-1234yf and othercomponent.

FIG. 2 is a schematic construction view illustrating a refrigeratingcycle system as an example of a heat cycle system of the presentinvention.

FIG. 3 is a diagram illustrating a composition range of one embodimentof a working fluid for heat cycle of the present invention in triangularcoordinates of a composition (mass %) of a mixture of HFO-1123,HFO-1234yf and HFC-32.

FIG. 4 is a cycle diagram illustrating the state change of a workingfluid in a refrigerating cycle system in FIG. 2 on a pressure-enthalpychart.

FIG. 5 is a graph showing the relation between the composition and thetemperature gradient of a mixed fluid of HFO-1123 and HFO-1234yf.

FIG. 6 is a graph showing the relation between the composition and thecoefficient of performance (relative to R410A) of a mixed fluid ofHFO-1123 and HFO-1234yf.

FIG. 7 is a graph showing the relation between the composition and therefrigerating capacity (relative to R410A) of a mixed fluid of HFO-1123and HFO-1234yf.

FIG. 8 is a graph showing the relation between the composition and thecritical temperature of a mixed fluid of HFO-1123 and HFO-1234yf.

DESCRIPTION OF EMBODIMENTS

Now, the present invention will be described in detail.

<Working Fluid>

The working fluid of the present invention is a working fluid for heatcycle, which contains HFO-1123 and HFO-1234yf, wherein the totalproportion of HFO-1123 and HFO-1234yf based on the entire amount of theworking fluid is from 70 to 100 mass %, and the proportion of HFO-1123based on the total amount of HFO-1123 and HFO-1234yf is from 35 to 95mass %.

As heat cycle, heat cycle by a heat exchanger such as a condenser or anevaporator may be used without any particular restriction.

The composition range of the present invention will be described belowas the composition range (S).

The composition range (S) of the working fluid for heat cycle of thepresent invention is shown in triangular coordinates in FIG. 1. Theworking fluid for heat cycle of the present invention is a mixed fluidcontaining HFO-1123 and HFO-1234yf and as the case requires, othercomponent. FIG. 1 illustrates triangular coordinates indicating thecomposition (mass %) of HFO-1123, HFO-1234yf and other component by therespective three sides, and a trapezoidal region surrounded by a heavysolid line including part of the base of the triangle corresponds to thecomposition range (S) of the working fluid of the present invention. InFIG. 1, “1123/1234” means the mass ratio of HFO-1123 to HFO-1234yf, and“1123+1234” means the total mass % of HFO-1123 and HFO-1234yf based onthe entire amount of the working fluid. Now, the composition of theworking fluid of the present invention will be described with referenceto FIG. 1 as needed.

Here, the global warming potential (100 years) of HFO-1234yf is 4 by avalue in Intergovernmental Panel on Climate Change (IPCC), Fourthassessment report (2007), and the global warming potential (100 years)of HFO-1123 is 0.3 as a value measured in accordance with IPCC Fourthassessment report. GWP in this specification is a value (100 years) inIPCC Fourth assessment report unless otherwise specified. Further, GWPof a mixture is represented by a weighted average by the compositionmass. For example, GWP of a mixture of HFO-1123 and HFO-1234yf in a massratio of 1:1 is calculated as (0.3+4)/2=2.15.

The working fluid of the present invention has a low GWP since itcontains HFO-1123 with a very low GWP and HFO-1234yf in a total contentof at least 70 mass %. In the triangular coordinates in FIG. 1, in acase where GWP of other component is higher than those of HFO-1123 andHFO-1234yf, as in the case of the after-mentioned saturated HFC forexample, the closer to the base, the lower the GWP. Further, in such acase, a composition with the minimum GWP of the working fluid of thepresent invention is a composition indicated by the lower left angle inthe trapezoid (composition range (S)) in FIG. 1, that is, such acomposition that the working fluid consists solely of HFO-1123 andHFO-1234yf in a proportion of HFO-1234yf of 5 mass % based on 95 mass %of HFO-1123.

The proportion of HFO-1123 based on the total amount of HFO-1123 andHFO-1234yf in the working fluid is from 35 to 95 mass %, preferably from40 to 95 mass %, more preferably from 50 to 90 mass %, furtherpreferably from 50 to 85 mass %, most preferably from 60 to 85 mass %.In the triangular coordinates in FIG. 1, the left side in the trapezoidindicating the composition range (S) indicates a boundary of1123/1234=95/5 mass %. The right side indicates a boundary of1123/1234=35/65 mass %. The upper side indicates a line of 1123+1234=70mass %, and the lower side (base) indicates a line of 1123+1234=100 mass%.

Within a range of the proportion of HFO-1123 based on the total amountof HFO-1123 and HFO-1234yf in the working fluid of at least 35 mass %,the temperature gradient is small, such being favorable. Within a rangeof at least 40 mass %, the temperature gradient is smaller, and such ispractically more favorable as an alternative to R410A. Further, within arange of the proportion of HFO-1123 based on the total amount ofHFO-1123 and HFO-1234yf in the working fluid of from 35 to 95 mass %,refrigerating cycle performance sufficient as an alternative toconventional R410A will be achieved also in view of the coefficient ofperformance, the refrigerating capacity and the critical temperature inaddition to the temperature gradient. By using such a working fluid ofthe present invention for heat cycle, practically sufficientrefrigerating capacity and coefficient of performance will be obtained.

The total content of HFO-1123 and HFO-1234yf based on 100 mass % of theworking fluid of the present invention is from 70 to 100 mass %. Whenthe total content of HFO-1123 and HFO-1234yf is within the above range,the efficiency will be further increased while maintaining certaincapacity when such a working fluid is used for heat cycle, and favorablecycle performance will be obtained. The total content of HFO-1123 andHFO-1234yf based on 100 mass % of the working fluid is preferably from80 to 100 mass %, more preferably from 90 to 100 mass %, furtherpreferably from 95 to 100 mass %.

As mentioned above, HFO-1123 and HFO-1234yf in the working fluid of thepresent invention are both HFOs and are compounds which have lessinfluence over global warming. Further, although HFO-1123 has excellentcapacity as a working fluid, but may not be sufficient in view of thecoefficient of performance as compared with other HFOs. Further, whenHFO-1123 is used alone, from the viewpoint of the critical temperature,sufficient refrigerating cycle performance may not be expected in somecases for an application in which R410A has been used.

Further, HFO-1123 is known to undergo self-decomposition when used aloneat high temperature or with an ignition source under high pressure.Therefore, an attempt to suppress self-decomposition reaction by mixingHFO-1123 with another component such as vinylidene fluoride to form amixture having a lowered content of HFO-1123 has been reported(Combustion, Explosion, and Shock Waves, Vol. 42, No 2, pp. 140-143,2006).

However, under the temperature and pressure conditions under whichHFO-1123 is used as a working fluid, a composition with which theworking fluid can be safely used while maintaining refrigerating cycleperformance of HFO-1123 has not been known. Accordingly, the presentinventor has confirmed that self-decomposition can be suppressed underthe temperature and pressure conditions under which a compositioncontaining HFO-1123 is used as a working fluid, when the content ofHFO-1123 based on the entire amount of the composition is at most 70 mol%.

<Evaluation of Self-Decomposition Property of HFO-1123>

The self-decomposition property was evaluated in equipment in accordancewith method A recommended as equipment for measurement of the combustionrange of a gas mixture containing halogen, by individual notificationsin High Pressure Gas Safety Act.

Specifically, a mixed fluid of HFO-1123 and HFO-1234yf, HFO-1123 andHFC-32 or HFO-1123, HFO-1234yf and HFC-32 in various proportions, isenclosed in a spherical pressure resistant reactor having an internalcapacity of 650 cm³ and having a predetermined temperature controlledfrom the outside to a predetermined pressure, and then a platinum wiredisposed in the interior was fused to apply an energy of about 30 J.Whether the self-decomposition reaction occurred or not was confirmed bymeasuring the temperature and pressure changes in the pressure resistantreactor after the application. A case where a pressure increase and atemperature increase were confirmed was evaluated as self-decompositionreaction occurred. The results are shown in Table 1 with respect tomixed fluids of HFO-1123 and HFO-1234yf, in Table 2 with respect tomixed fluids of HFO-1123 and HFC-32, and in Table 3 with respect tomixed fluids of HFO-1123, HFO-1234yf and HFC-32. The pressure in Tables1, 2 and 3 is the gage pressure.

TABLE 1 Pressure Temperature [MPaG] [° C.] Self- HFO-1123/HFO-1234yfBefore After Before After decomposition [mass %/mass %] [mol %/mol %]ignition ignition ignition ignition reaction 52/48 60/40 0.98 0.98 250250.2 Nil 63/37 70/30 0.98 0.98 250 250.2 Nil 74/26 80/20 0.98 4.00 250291.6 Occurred 87/13 90/10 0.98 4.80 250 291.1 Occurred

TABLE 2 Pressure Temperature [MPaG] [° C.] Self- HFO-1123/HFC-32 BeforeAfter Before After decomposition [mass %/mass %] [mol %/mol %] ignitionignition ignition ignition reaction 70/30 60/40 0.98 0.98 250 250.5 Nil80/20 72/28 0.98 0.98 250 250.4 Nil 85/15 78/22 0.98 4.60 250 290.0Occurred

TABLE 3 Pressure Temperature HFO-1123/HFO-1234yf/HFC-32 [MPaG] [° C.]Self- [mass %/mass %/mass [mol %/mol %/mol Before After Before Afterdecomposition %] %] ignition ignition ignition ignition reaction70/10/20 64/7/29 0.98 0.98 250 250.5 Nil 70/20/10 70/14/16 0.98 0.98 250250.5 Nil 80/10/10 78/7/15 0.98 4.00 250 289.5 Occurred

The working fluid of the present invention may be used for a heat cyclesystem even though it is a self-decomposable composition, bysufficiently careful handling depending upon the use conditions.However, a composition range of the working fluid with high safety andwith high refrigerating cycle performance as well, can be achieved byselecting a composition range excluding the composition range withself-decomposition property thus confirmed from the composition range(S) of the working fluid of the present invention, that is, by selectinga composition range in which the composition range (S) of the workingfluid of the present invention and a region with a content of HFO-1123based on the entire amount of the working fluid of at most 70 mol %overlap.

HFO-1234yf is a HFO having the refrigerating capacity and thecoefficient of performance as a working fluid in a balanced manner.Although the critical temperature (94.7° C.) of HFO-1234yf is high ascompared with HFO-1123, its capacity when used alone is insufficient ascompared with R410A.

HFO-1123 and HFO-1234yf in the working fluid of the present inventionare not in an azeotropic state. In general, a non-azeotropic mixturefluid as a working fluid has such properties that the initiationtemperature and the completion temperature of evaporation in anevaporator or of condensation in a condenser, for example, as a heatexchanger, differ from each other, that is, it has a temperaturegradient. Accordingly, since the working fluid of the present inventionmainly contains HFO-1123 and HFO-1234yf, that is, it contains HFO-1123and HFO-1234yf in a total content of at least 70 mass % based on theentire amount of the working fluid, it has a temperature gradient.

The influence in a heat cycle system when the working fluid of thepresent invention has a temperature gradient will be described withreference to a case where the working fluid is used for a heat cyclesystem shown in FIG. 2. FIG. 2 is a schematic construction viewillustrating a refrigerating cycle system as an example of a heat cyclesystem of the present invention.

A refrigerating cycle system 10 comprises a compressor 11 to compress aworking fluid (vapor), a condenser 12 to cool and liquefy the workingfluid vapor discharged from the compressor 11, an expansion valve 13 tolet the working fluid (liquid) discharged from the condenser 12 expand,and an evaporator 14 to heat and vaporize the working fluid in a liquidstate discharged from the expansion valve 13.

In the refrigerating cycle system 10, the temperature of the workingfluid increases from an inlet toward an outlet of the evaporator 14 atthe time of evaporation, and on the contrary, the temperature decreasesfrom an inlet toward an outlet of the condenser 12 at the time ofcondensation. In the refrigerating cycle system 10, such is achieved byheat exchange between the working fluid and a heat source fluid such aswater or the air flowing to face the working fluid in the evaporator 14or the condenser 12. The heat source fluid is represented by “E→E” inthe evaporator 14 and by “F→F” in the condenser 12 in the refrigeratingcycle system 10.

Here, when a single refrigerant is used, since there is no temperaturegradient, the temperature difference between the outlet temperature andthe inlet temperature of the evaporator 14 is substantially constant,however, when a non-azeotropic mixture fluid is used, the temperaturedifference will not be constant. For example, in a case where theworking fluid is to be evaporated at 0° C. in the evaporator 14, theinlet temperature is lower than 0° C., and frosting may occur in theevaporator 14. Particularly, the larger the temperature gradient, thelower the inlet temperature and the more frosting is likely to occur.

Further, in a case where a non-azeotropic mixture fluid with a largetemperature gradient is used for the refrigerating cycle system 10,since the compositions of the gaseous phase and the liquid phase aresignificantly different from each other, if the non-azeotropic mixturefluid circulating in the system 10 leaks out, the composition of thenon-azeotropic mixture fluid circulating in the system 10 maysignificantly change as between before and after the leakage.

Further, for example, as shown in the refrigerating cycle system 10,usually in the heat cycle system, the heat exchange efficiency is to beimproved by making the working fluid and the heat source fluid such aswater or the air flowing in heat exchangers such as the evaporator 14and the condenser 12 flow in counter-current flow. Here, since thetemperature difference of the heat source fluid is small usually in along-term stable operation state except for at the time of start-up, itis difficult to obtain a heat cycle system with a good energy efficiencywith a non-azeotropic mixture fluid with a large temperature gradient.Accordingly, a non-azeotropic mixture fluid with an appropriatetemperature gradient is desired.

The composition range and the content range of the combination ofHFO-1123 and HFO-1234yf in the working fluid of the present inventionare ranges within which the working fluid has a practical temperaturegradient.

The temperature gradient of the working fluid is preferably at most 9.5°C., more preferably at most 9° C., further preferably at most 8.4° C.,most preferably at most 7.2° C.

[Optional Component]

The working fluid of the present invention may optionally contain acompound commonly used for a working fluid, in addition to HFO-1123 andHFO-1234yf, within a range not to impair effects of the presentinvention. Even when the working fluid of the present invention containsan optional compound (which will be referred to as an optionalcomponent), the temperature gradient of the working fluid will not be 0and the working fluid has a considerable temperature gradient. Thetemperature gradient of the working fluid of the present inventionvaries depending upon the mixture ratio of HFO-1123 and HFO-1234yf andthe optional component contained as the case requires.

The optional component is preferably a HFC or a HFO (a HFC having acarbon-carbon double bond) other than HFO-1123 and HFO-1234yf.

(HFC)

As the HFC as the optional component, a HFC having an effect to decreasethe temperature gradient, to improve the capacity or to further increasethe efficiency, when used in combination with HFO-1123 and HFO-1234yffor heat cycle, is used. When the working fluid of the present inventioncontains such a HFC, more favorable cycle performance will be obtained.

A HFC is known to have a high GWP as compared with HFO-1123 andHFO-1234yf. Accordingly, a HFC to be used as the optional component isselected with a view to adjusting the GWP within an acceptable range, inaddition to improving cycle performance as the working fluid.

As a HFC which has less influence over the ozone layer and which hasless influence over global warming, specifically preferred is a C₁₋₅HFC. The HFC may be linear, branched or cyclic.

The HFC may, for example, be difluoromethane (HFC-32), difluoroethane,trifluoroethane, tetrafluoroethane, pentafluoroethane (HFC-125),pentafluoropropane, hexafluoropropane, heptafluoropropane,pentafluorobutane or heptafluorocyclopentane.

Particularly, in view of less influence over the ozone layer andexcellent refrigerating cycle performance, the HFC is preferably HFC-32,1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a),1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,2-tetrafluoroethane(HFC-134a) or HFC-125, more preferably HFC-32, HFC-134a or HFC-125.

The HFC may be used alone or in combination of two or more.

With respect to GWP of the above preferred HFC, GWP of HFC-32 is 675,GWP of HFC-134a is 1,430, and GWP of HFC-125 is 3,500. With a view tosuppressing the GWP of the obtainable working fluid to be low, the HFCas the optional component is most preferably HFC-32.

In a case where HFO-1123, HFO-1234yf and HFC-32 are combined for theworking fluid of the present invention, it is preferred that thecomposition range (S) of the working fluid of the present invention issatisfied and that based on the total amount of HFO-1123, HFO-1234yf andHFC-32, the proportion of HFO-1123 is from 30 to 80 mass %, theproportion of HFO-1234yf is at most 40 mass %, and the proportion ofHFC-32 is at most 30 mass %. This composition range will be describedbelow as the composition range (P).

The composition range (P) in a case where the working fluid for heatcycle of the present invention comprises HFO-1123, HFO-1234yf and HFC-32is shown in triangular coordinates in FIG. 3. That is, FIG. 3illustrates triangular coordinates indicating the composition (mass %)of HFO-1123, HFO-1234yf and HFC-32 by the respective three sides, and apentangular region surrounded by a heavy solid line, one side of whichis slightly on the inner side of the base of the triangular, correspondsto the composition range (P) of the preferred working fluid of thepresent invention.

The sides (P1) to (P5) of the pentagon indicating the composition range(P) in FIG. 3 respectively indicate boundaries of the following ranges.In the following formulae, abbreviated names of the respective compoundsindicate the proportions (mass %) of the respective compounds based onthe entire amount of the working fluid, that is, the total amount ofHFO-1123, HFO-1234yf and HFC-32.

(P1) 70 mass %≤HFO-1123+HFO-1234yf, and HFC-32≤30 mass %

(P2) HFO-1123/HFO-1234yf≤95/5 mass %

(P3) HFO-1123≤80 mass %

(P4) 0 mass %<HFC-32

(P5) HFO-1234yf≤40 mass % As described above, GWPs of HFO-1123,HFO-1234yf and HFC-32 are respectively 0.3, 4 and 675. The compositionwith which GWP is highest in the composition range (P) is thecomposition at the upper right angle of the pentagon, that is, thecomposition comprising HFO-1123:HFO-1234yf:HFC-32 of 30 mass %:40 mass%:30 mass %, and GWP with the composition is calculated as(0.3×30+4×40+675×30)/100=204.19. The working fluid in such a compositionrange (P) is a working fluid having respective characteristics ofHFO-1123, HFO-1234yf and HFC-32 in a balanced manner, and having defectsof the respective components suppressed. That is, the working fluid inthe composition range (P) is a working fluid which has a low GWP, has asmall temperature gradient and has a certain performance and efficiencywhen used for heat cycle, and thus with such a working fluid, favorablecycle performance will be obtained.

Further, in the same manner as above, by selecting a composition rangeexcluding the composition range with self-decomposition property asconfirmed above from such a composition range (P), that is, by selectinga composition range in which the composition range (P) and a region witha content of HFO-1123 based on the entire amount of the working fluid ofless than 70 mol % overlap, a composition range of the working fluidwith high safety and with high refrigerating cycle performance as well,can be achieved.

In a case where the working fluid of the present invention comprisesthree compounds of HFO-1123, HFO-1234yf and HFC-32, a more preferredcomposition may be a composition containing HFO-1123 in a proportion offrom 30 to 70 mass %, HFO-1234yf in a proportion of from 4 to 40 mass %,and HFC-32 in a proportion of higher than 0 to 30 mass %, based on thetotal amount of HFO-1123, HFO-1234yf and HFC-32 and having a content ofHFO-1123 based on the entire amount of the working fluid of at most 70mol %, within a range of the composition range (P). From the viewpointof the relative coefficient of performance, the content of HFC-32 ispreferably at least 5 mass %, more preferably at least 8 mass %.

(HFO Other than HFO-1123 and HFO-1234yf)

The HFO as the optional component may, for example, be1,2-difluoroethylene (HFO-1132), 2-fluoropropene (HFO-1261yf),1,1,2-trifluoropropene (HFO-1243yc), trans-1,2,3,3,3-pentafluoropropene(HFO-1225ye(E)), cis-1,2,3,3,3-pentafluoropropene (HFO-1225ye(Z)),trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)),cis-1,3,3,3-tetrafluoropropene (HFO-1234ze(Z)) or 3,3,3-trifluoropropene(HFO-1243zf).

Particularly, the HFO as the optional component is, in view of a highcritical temperature and excellent safety and coefficient ofperformance, preferably HFO-1234ze(E) or HFO-1234ze(Z), more preferablyHFO-1234ze(E).

The HFO other than HFO-1123 and HFO-1234yf may be used alone or incombination of two or more.

In a case where the working fluid of the present invention contains theHFC and/or the HFO other than HFO-1123 and HFO-1234yf as the optionalcomponent, the total content of the HFC and the HFO other than HFO-1123and HFO-1234yf per 100 mass % of the working fluid is at most 30 mass %,preferably from 1 to 20 mass %, more preferably from 1 to 10 mass %,further preferably from 2 to 8 mass %. The total content of the HFC andthe HFO other than HFO-1123 and HFO-1234yf in the working fluid isproperly adjusted within the above range depending upon the type of theHFC and the HFO other than HFO-1123 and HFO-1234yf to be used, with aview to decreasing the temperature gradient, improving the capacity orfurther increasing the efficiency when used for heat cycle incombination with HFO-1123 and HFO-1234yf, and further considering theglobal warming potential.

(Other Optional Component)

The working fluid of the present invention may contain, other than theabove optional component, another optional component such as carbondioxide, a hydrocarbon, a chlorofluoroolefin (CFO) or ahydrochlorofluoroolefin (HCFO). Such another optional component ispreferably a component which has less influence over the ozone layer andwhich has less influence over global warming.

The hydrocarbon may, for example, be propane, propylene, cyclopropane,butane, isobutane, pentane or isopentane.

The hydrocarbon may be used alone or in combination of two or more.

In a case where the working fluid of the present invention contains ahydrocarbon, its content is at most 30 mass %, preferably from 1 to 20mass %, more preferably from 1 to 10 mass %, further preferably from 3to 8 mass % per 100 mass % of the working fluid. When the content of thehydrocarbon is at least the lower limit, the solubility of a minerallubricating oil in the working fluid will be favorable.

The CFO may, for example, be chlorofluoropropene orchlorofluoroethylene. With a view to suppressing flammability of theworking fluid without significantly decreasing the cycle performance ofthe working fluid of the present invention, the CFO is preferably1,1-dichloro-2,3,3,3-tetrafluoropropene (CFO-1214ya),1,3-dichloro-1,2,3,3-tetrafluoropropene (CFO-1214yb) or1,2-dichloro-1,2-difluoroethylene (CFO-1112).

The CFO may be used alone or in combination of two or more.

When the working fluid of the present invention contains the CFO, itscontent is at most 30 mass %, preferably from 1 to 20 mass %, morepreferably from 1 to 10 mass %, further preferably from 2 to 8 mass %per 100 mass % of the working fluid. When the content of the CFO is atleast the lower limit, the flammability of the working fluid tends to besuppressed. When the content of the CFO is at most the upper limit,favorable cycle performance is likely to be obtained.

The HCFO may, for example, be hydrochlorofluoropropene orhydrochlorofluoroethylene. With a view to suppressing the flammabilityof the working fluid without significantly decreasing the cycleperformance of the working fluid of the present invention, the HCFO ispreferably 1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd) or1-chloro-1,2-difluoroethylene (HCFO-1122).

The HCFO may be used alone or in combination of two or more.

In a case where the working fluid of the present invention contains theHCFO, the content of the HCFO per 100 mass % of the working fluid of thepresent invention is at most 30 mass %, preferably from 1 to 20 mass %,more preferably from 1 to 10 mass %, further preferably from 2 to 8 mass%. When the content of the HCFO is at least the lower limit, theflammability of the working fluid tends to be suppressed. When thecontent of the HCFO is at most the upper limit, favorable cycleperformance is likely to be obtained.

When the working fluid of the present invention contains the aboveoptional component and another optional component, their total contentis at most 30 mass % per 100 mass % of the working fluid.

The above-described working fluid of the present invention is a workingfluid obtained by mixing HFO-1123 which is excellent in the performanceas the working fluid and HFO-1234yf which has the capacity and theefficiency as the working fluid in a balanced manner, which are bothHFOs having less influence over global warming, in combination in such aproportion as to improve the cycle performance as compared with a casewhere they are respectively used alone, considering the temperaturegradient in a mixed fluid of them, and has practically sufficient cycleperformance while suppressing the influence over global warming.

[Application to Heat Cycle System] (Composition for Heat Cycle System)

The working fluid of the present invention may be used, in applicationto a heat cycle system, as the composition for a heat cycle system ofthe present invention usually as mixed with a lubricating oil. Thecomposition for a heat cycle system of the present invention comprisingthe working fluid of the present invention and a lubricating oil mayfurther contain known additives such as a stabilizer and a leakdetecting substance.

(Lubricating Oil)

As a lubricating oil, a known lubricating oil which has been used forthe composition for a heat cycle system together with a working fluidcomprising a halogenated hydrocarbon may be used without any particularrestrictions. The lubricating oil may, for example, be specifically anoxygen-containing synthetic oil (such as an ester lubricating oil or anether lubricating oil), a fluorinated lubricating oil, a minerallubricating oil or a hydrocarbon synthetic oil.

The ester lubricating oil may, for example, be a dibasic acid ester oil,a polyol ester oil, a complex ester oil or a polyol carbonate oil.

The dibasic acid ester oil is preferably an ester of a C₅₋₁₀ dibasicacid (such as glutaric acid, adipic acid, pimelic acid, suberic acid,azelaic acid or sebacic acid) with a C₁₋₁₅ monohydric alcohol which islinear or has a branched alkyl group (such as methanol, ethanol,propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol,decanol, undecanol, dodecanol, tridecanol, tetradecanol orpentadecanol). Specifically, ditridecyl glutarate, di(2-ethylhexyl)adipate, diisodecyl adipate, ditridecyl adipate or di(3-ethylhexyl)sebacate may, for example, be mentioned.

The polyol ester oil is preferably an ester of a diol (such as ethyleneglycol, 1,3-propanediol, propylene glycol, 1,4-butanediol,1,2-butandiol, 1,5-pentadiol, neopentyl glycol, 1,7-heptanediol or1,12-dodecanediol) or a polyol having from 3 to 20 hydroxy groups (suchas trimethylolethane, trimethylolpropane, trimethylolbutane,pentaerythritol, glycerol, sorbitol, sorbitan or sorbitol/glycerincondensate) with a C₆₋₂₀ fatty acid (such as a linear or branched fattyacid such as hexanoic acid, heptanoic acid, octanoic acid, nonanoicacid, decanoic acid, undecanoic acid, dodecanoic acid, eicosanoic acidor oleic acid, or a so-called neo acid having a quaternary a carbonatom).

The polyol ester oil may have a free hydroxy group.

The polyol ester oil is preferably an ester (such as trimethylolpropanetripelargonate, pentaerythritol 2-ethylhexanoate or pentaerythritoltetrapelargonate) of a hindered alcohol (such as neopentyl glycol,trimethylolethane, trimethylolpropane, trimethylolbutane orpentaerythritol).

The complex ester oil is an ester of a fatty acid and a dibasic acid,with a monohydric alcohol and a polyol. The fatty acid, the dibasicacid, the monohydric alcohol and the polyol may be as defined above.

The polyol carbonate oil is an ester of carbonic acid with a polyol.

The polyol may be the above-described diol or the above-describedpolyol.

Further, the polyol carbonate oil may be a ring-opening polymer of acyclic alkylene carbonate.

The ether lubricating oil may be a polyvinyl ether oil or apolyoxyalkylene oil.

The polyvinyl ether oil may be one obtained by polymerizing a vinylether monomer such as an alkyl vinyl ether, or a copolymer obtained bycopolymerizing a vinyl ether monomer and a hydrocarbon monomer having anolefinic double bond.

The vinyl ether monomer may be used alone or in combination of two ormore.

The hydrocarbon monomer having an olefinic double bond may, for example,be ethylene, propylene, various forms of butene, various forms ofpentene, various forms of hexene, various forms of heptene, variousforms of octene, diisobutylene, triisobutylene, styrene, α-methylstyreneor alkyl-substituted styrene. The hydrocarbon monomer having an olefinicdouble bond may be used alone or in combination of two or more.

The polyvinyl ether copolymer may be either of a block copolymer and arandom copolymer. The polyvinyl ether oil may be used alone or incombination of two or more.

The polyoxyalkylene oil may, for example, be a polyoxyalkylene monool, apolyoxyalkylene polyol, an alkyl ether of a polyoxyalkylene monool or apolyoxyalkylene polyol, or an ester of a polyoxyalkylene monool or apolyoxyalkylene polyol.

The polyoxyalkylene monool or the polyoxyalkylene polyol may be oneobtained by e.g. a method of subjecting a C₂₋₄ alkylene oxide (such asethylene oxide or propylene oxide) to ring-opening additionpolymerization to an initiator such as water or a hydroxygroup-containing compound in the presence of a catalyst such as analkali hydroxide. Further, one molecule of the polyoxyalkylene chain maycontain single oxyalkylene units or two or more types of oxyalkyleneunits. It is preferred that at least oxypropylene units are contained inone molecule.

The initiator to be used for the reaction may, for example, be water, amonohydric alcohol such as methanol or butanol, or a polyhydric alcoholsuch as ethylene glycol, propylene glycol, pentaerythritol or glycerol.

The polyoxyalkylene oil is preferably an alkyl ether or an ester of apolyoxyalkylene monool or polyoxyalkylene polyol. Further, thepolyoxyalkylene polyol is preferably a polyoxyalkylene glycol.Particularly preferred is an alkyl ether of a polyoxyalkylene glycolhaving the terminal hydroxy group of the polyoxyalkylene glycol cappedwith an alkyl group such as a methyl group, which is called a polyglycoloil.

The fluorinated lubricating oil may, for example, be a compound havinghydrogen atoms of a synthetic oil (such as the after-mentioned mineraloil, poly-α-olefin, alkylbenzene or alkylnaphthalene) substituted byfluorine atoms, a perfluoropolyether oil or a fluorinated silicone oil.

The mineral lubricating oil may, for example, be a naphthene mineral oilor a paraffin mineral oil obtained by purifying a lubricating oilfraction obtained by atmospheric distillation or vacuum distillation ofcrude oil by a purification treatment (such as solvent deasphalting,solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing,hydrotreating or clay treatment) optionally in combination.

The hydrocarbon synthetic oil may, for example, be a poly-α-olefin, analkylbenzene or an alkylnaphthalene.

The lubricating oil may be used alone or in combination of two or more.

The lubricating oil is preferably at least one member selected from apolyol ester oil, a polyvinyl ether oil and a polyglycol oil.

The amount of the lubricating oil is not limited within a range not toremarkably decrease the effects of the present invention, and ispreferably from 10 to 100 parts by mass, more preferably from 20 to 50parts by mass, per 100 parts by mass of the working fluid.

(Stabilizer)

The stabilizer is a component which improves the stability of theworking fluid against heat and oxidation. As the stabilizer, a knownstabilizer which has been used for a heat cycle system together with aworking fluid comprising a halogenated hydrocarbon, for example, anoxidation resistance-improving agent, a heat resistance-improving agentor a metal deactivator, may be used without any particular restrictions.

The oxidation resistance-improving agent and the heatresistance-improving agent may, for example, beN,N′-diphenylphenylenediamine, p-octyldiphenylamine,p,p′-dioctyldiphenylamine, N-phenyl-1-naphthyamine,N-phenyl-2-naphthylamine, N-(p-dodecyl)phenyl-2-naphthylamine,di-1-naphthylamine, di-2-naphthylamine, N-alkylphenothiazine,6-(t-butyl)phenol, 2,6-di-(t-butyl)phenol,4-methyl-2,6-di-(t-butyl)phenol or4,4′-methylenebis(2,6-di-t-butylphenol). Each of the oxidationresistance-improving agent and the heat resistance-improving agent maybe used alone or in combination of two or more.

The metal deactivator may, for example, be imidazole, benzimidazole,2-mercaptobenzothiazole, 2,5-dimercaptothiadiazole,salicylidene-propylenediamine, pyrazole, benzotriazole, tritriazole,2-methylbenzamidazole, 3,5-dimethylpyrazole, methylenebis-benzotriazole,an organic acid or an ester thereof, a primary, secondary or tertiaryaliphatic amine, an amine salt of an organic acid or inorganic acid, aheterocyclic nitrogen-containing compound, an amine salt of an alkylphosphate, or a derivative thereof.

The amount of the stabilizer is not limited within a range not toremarkably decrease the effects of the present invention, and ispreferably at most 5 parts by mass, more preferably at most 1 part bymass per 100 parts by mass of the working fluid.

(Leak Detecting Substance)

The leak detecting substance may, for example, be an ultravioletfluorescent dye, an odor gas or an odor masking agent.

The ultraviolet fluorescent dye may be known ultraviolet fluorescentdyes which have been used for a heat cycle system together with aworking fluid comprising a halogenated hydrocarbon, such as dyes asdisclosed in e.g. U.S. Pat. No. 4,249,412, JP-A-10-502737,JP-A-2007-511645, JP-A-2008-500437 and JP-A-2008-531836.

The odor masking agent may be known perfumes which have been used for aheat cycle system together with a working fluid comprising a halogenatedhydrocarbon, such as perfumes as disclosed in e.g. JP-A-2008-500437 andJP-A-2008-531836.

In a case where the leak detecting substance is used, a solubilizingagent which improves the solubility of the leak detecting substance inthe working fluid may be used. The solubilizing agent may be ones asdisclosed in e.g. JP-A-2007-511645, JP-A-2008-500437 andJP-A-2008-531836.

The amount of the leak detecting substance is not particularly limitedwithin a range not to remarkably decrease the effects of the presentinvention, and is preferably at most 2 parts by mass, more preferably atmost 0.5 part by mass per 100 parts by mass of the working fluid.

<Heat Cycle System>

The heat cycle system of the present invention is a system employing theworking fluid of the present invention. When the working fluid of thepresent invention is applied to a heat cycle system, usually the workingfluid is applied as contained in the composition for a heat cyclesystem. The heat cycle system of the present invention may be a heatpump system utilizing heat obtained by a condenser or may be arefrigerating cycle system utilizing coldness obtained by an evaporator.

The heat cycle system of the present invention may, for example, bespecifically a refrigerator, an air-conditioning apparatus, a powergeneration system, a heat transfer apparatus and a secondary coolingmachine. Among them, the heat cycle system of the present invention,which stably exhibits heat cycle performance in a working environment athigher temperature, is preferably employed as an air-conditioningapparatus to be disposed outdoors in many cases. Further, the heat cyclesystem of the present invention is preferably employed also for arefrigerating system.

The air-conditioning apparatus may, for example, be specifically a roomair-conditioner, a package air-conditioner (such as a store packageair-conditioner, a building package air-conditioner or a plant packageair-condition, a gas engine heat pump, a train air-conditioning systemor an automobile air-conditioning system.

The refrigerator may, for example, be specifically a showcase (such as abuilt-in showcase or a separate showcase), an industrial fridge freezer,a vending machine or an ice making machine.

The power generation system is preferably a power generation system byRankine cycle system.

The power generation system may, for example, be specifically a systemwherein in an evaporator, a working fluid is heated by e.g. geothermalenergy, solar heat or waste heat in a medium-to-high temperature rangeat a level of from 50 to 200° C., and the vaporized working fluid in ahigh temperature and high pressure state is adiabatically expanded by anexpansion device, so that a power generator is driven by the workgenerated by the adiabatic expansion to carry out power generation.

Further, the heat cycle system of the present invention may be a heattransport apparatus. The heat transport apparatus is preferably a latentheat transport apparatus.

The latent heat transport apparatus may, for example, be a heat pipeconducting latent heat transport utilizing evaporation, boiling,condensation, etc. of a working fluid filled in an apparatus, and atwo-phase closed thermosiphon. A heat pipe is applied to a relativelysmall-sized cooling apparatus such as a cooling apparatus of a heatingportion of a semiconductor device and electronic equipment. A two-phaseclosed thermosiphon is widely used for a gas/gas heat exchanger, toaccelerate snow melting and to prevent freezing of roads, since it doesnot require a wick and its structure is simple.

Now, as an example of the heat cycle system according the embodiment ofthe present invention, a refrigerating cycle system will be describedwith reference to a refrigerating cycle system 10 which has been roughlydescribed above, of which the schematic construction view is shown inFIG. 2, as an example. A refrigerating cycle system is a systemutilizing coldness obtained by an evaporator.

A refrigerating cycle system 10 shown in FIG. 2 is a system generallycomprising a compressor 11 to compress a working fluid vapor A to form ahigh temperature/high pressure working fluid vapor B, a condenser 12 tocool and liquefy the working fluid vapor B discharged from thecompressor 11 to form a low temperature/high pressure working fluid C,an expansion valve 13 to let the working fluid C discharged from thecondenser 12 expand to form a low temperature/low pressure working fluidD, an evaporator 14 to heat the working fluid D discharged from theexpansion valve 13 to form a high temperature/low pressure working fluidvapor A, a pump 15 to supply a load fluid E to the evaporator 14, and apump 16 to supply a fluid F to the condenser 12.

In the refrigerating cycle system 10, a cycle of the following (i) to(iv) is repeated.

(i) A working fluid vapor A discharged from an evaporator 14 iscompressed by a compressor 11 to form a high temperature/high pressureworking fluid vapor B (hereinafter referred to as “AB process”).

(ii) The working fluid vapor B discharged from the compressor 11 iscooled and liquefied by a fluid F in a condenser 12 to form a lowtemperature/high pressure working fluid C. At that time, the fluid F isheated to form a fluid F′, which is discharged from the condenser 12(hereinafter referred to as “BC process”).

(iii) The working fluid C discharged from the condenser 12 is expandedin an expansion valve 13 to form a low temperature/low pressure workingfluid D (hereinafter referred to as “CD process”).

(iv) The working fluid D discharged from the expansion valve 13 isheated by a load fluid E in an evaporator 14 to form a hightemperature/low pressure working fluid vapor A. At that time, the loadfluid E is cooled and becomes a load fluid E′, which is discharged fromthe evaporator 14 (hereinafter referred to as “DA process”).

The refrigerating cycle system 10 is a cycle system comprising anadiabatic isentropic change, an isenthalpic change and an isobaricchange. The state change of the working fluid, as represented on apressure enthalpy chart (curve) as shown in FIG. 4, may be representedas a trapezoid having points A, B, C and D as vertexes.

The AB process is a process wherein adiabatic compression is carried outby the compressor 11 to change the high temperature/low pressure workingfluid vapor A to a high temperature/high pressure working fluid vapor B,and is represented by the line AB in FIG. 4.

The BC process is a process wherein isobaric cooling is carried out inthe condenser 12 to change the high temperature/high pressure workingfluid vapor B to a low temperature/high pressure working fluid C and isrepresented by the BC line in FIG. 4. The pressure in this process isthe condensation pressure. Of the two intersection points of thepressure enthalpy chart and the BC line, the intersection point T₁ onthe high enthalpy side is the condensing temperature, and theintersection point T₂ on the low enthalpy side is the condensationboiling point temperature. Here, the temperature gradient of anon-azeotropic mixture fluid such as a mixture of HFO-1123 andHFO-1234yf, is represented by the difference between T₁ and T₂.

The CD process is a process wherein isenthalpic expansion is carried outby the expansion valve 13 to change the low temperature/high pressureworking fluid C to a low temperature/low pressure working fluid D and ispresented by the CD line in FIG. 4. T₂-T₃ corresponds to thesupercoiling degree (hereinafter referred to as “SC” as the caserequires) of the working fluid in the cycle of (i) to (iv), where T₃ isthe temperature of the low temperature/high pressure working fluid C.

The DA process is a process wherein isobaric heating is carried out inthe evaporator 14 to have the low temperature/low pressure working fluidD returned to a high temperature/low pressure working fluid vapor A, andis represented by the DA line in FIG. 4. The pressure in this process isthe evaporation pressure. Of the two intersection points of the pressureenthalpy chart and the DA line, the intersection point 16 on the highenthalpy side is the evaporation temperature. T₇-T₆ corresponds to thedegree of superheat (hereinafter referred to as “SH” as the caserequires) of the working fluid in the cycle of (i) to (iv), where T₇ isthe temperature of the working fluid vapor A. T₄ indicates thetemperature of the working fluid D.

Here, cycle performance of the working fluid is evaluated, for example,by the refrigerating capacity (hereinafter referred to as “Q” as thecase requires) and the coefficient of performance (hereinafter referredto as “COP” as the case requires) of the working fluid. Q and COP of theworking fluid are obtained respectively in accordance with the followingformulae (1) and (2) from enthalpies h_(A), h_(B), h_(C) and h_(D) inthe respective states A (after evaporation, high temperature and lowpressure), B (after compression, high temperature and high pressure), C(after condensation, low temperature and high pressure) and D (afterexpansion, low temperature and low pressure):

Q=h _(A) −h _(D)  (1)

COP=Q/compression work=(h _(A) −h _(D))/(h _(B) −h _(A))  (3)

COP means the efficiency in the refrigerating cycle system, and a higherCOP means that a higher output, for example, Q, can be obtained by asmaller input, for example, an electric energy required to operate acompressor.

Further, Q means a capacity to freeze a load fluid, and a higher Q meansthat more works can be done in the same system. In other words, it meansthat with a working fluid having a higher Q, the desired performance canbe obtained with a smaller amount, whereby the system can be downsized.

In the heat cycle system of the present invention using the workingfluid of the present invention, in a refrigerating cycle system 10 shownin FIG. 2 for example, as compared with a case where R410 (a mixture ofHFC-32 and HFC-125 in a mass ratio of 1:1) which has been commonly usedfor an air-conditioning apparatus or the like, it is possible to achievehigh levels of Q and COP, i.e. equal to or higher than those of R410A,while remarkably suppressing the global worming potential.

At the time of operation of the heat cycle system, in order to avoiddrawbacks due to inclusion of moisture or inclusion of non-condensinggas such as oxygen, it is preferred to provide a means to suppress suchinclusion.

If moisture is included in the heat cycle system, a problem may occurparticularly when the heat cycle system is used at low temperature. Forexample, problems such as freezing in a capillary tube, hydrolysis ofthe working fluid or the lubricating oil, deterioration of materials byan acid component formed in the cycle, formation of contaminants, etc.may arise. Particularly, if the lubricating oil is a polyglycol oil or apolyol ester oil, it has extremely high moisture absorbing propertiesand is likely to undergo hydrolysis, and inclusion of moisture decreasesproperties of the lubricating oil and may be a great cause to impair thelong term reliability of a compressor. Accordingly, in order to suppresshydrolysis of the lubricating oil, it is necessary to control themoisture concentration in the heat cycle system.

As a method of controlling the moisture concentration in the heat cyclesystem, a method of using a moisture-removing means such as adesiccating agent (such as silica gel, activated aluminum or zeolite)may be mentioned. The desiccating agent is preferably brought intocontact with the working fluid in a liquid state, in view of thedehydration efficiency. For example, the desiccating agent is located atthe outlet of the condenser 12 or at the inlet of the evaporator 14 tobe brought into contact with the working fluid.

The desiccating agent is preferably a zeolite desiccating agent in viewof chemical reactivity of the desiccating agent and the working fluid,and the moisture absorption capacity of the desiccating agent.

The zeolite desiccating agent is, in a case where a lubricating oilhaving a large moisture absorption as compared with a conventionalmineral lubricating oil is used, preferably a zeolite desiccating agentcontaining a compound represented by the following formula (3) as themain component in view of excellent moisture absorption capacity.

M_(2/n)O.Al₂O₃ .xSiO₂ .yH₂O  (3)

wherein M is a group 1 element such as Na or K or a group 2 element suchas Ca, n is the valence of M, and x and y are values determined by thecrystal structure. The pore size can be adjusted by changing M.

To select the desiccating agent, the pore size and the fracture strengthare important.

In a case where a desiccating agent having a pore size larger than themolecular size of the working fluid is used, the working fluid isadsorbed in the desiccating agent and as a result, chemical reactionbetween the working fluid and the desiccating agent will occur, thusleading to undesired phenomena such as formation of non-condensing gas,a decrease in the strength of the desiccating agent, and a decrease inthe adsorption capacity.

Accordingly, it is preferred to use as the desiccating agent a zeolitedesiccating agent having a small pore size. Particularly preferred issodium/potassium type A synthetic zeolite having a pore size of at most3.5 Å. By using a sodium/potassium type A synthetic zeolite having apore size smaller than the molecular size of the working fluid, it ispossible to selectively adsorb and remove only moisture in the heatcycle system without adsorbing the working fluid. In other words, theworking fluid is less likely to be adsorbed in the desiccating agent,whereby heat decomposition is less likely to occur and as a result,deterioration of materials constituting the heat cycle system andformation of contaminants can be suppressed.

The size of the zeolite desiccating agent is preferably from about 0.5to about 5 mm, since if it is too small, a valve or a thin portion inpipelines of the heat cycle system may be clogged, and if it is toolarge, the drying capacity will be decreased. Its shape is preferablygranular or cylindrical.

The zeolite desiccating agent may be formed into an optional shape bysolidifying powdery zeolite by a binding agent (such as bentonite). Solong as the desiccating agent is composed mainly of the zeolitedesiccating agent, other desiccating agent (such as silica gel oractivated alumina) may be used in combination.

The proportion of the zeolite desiccating agent based on the workingfluid is not particularly limited.

If non-condensing gas is included in the heat cycle system, it hasadverse effects such as heat transfer failure in the condenser or theevaporator and an increase in the working pressure, and it is necessaryto suppress its inclusion as far as possible. Particularly, oxygen whichis one of non-condensing gases reacts with the working fluid or thelubricating oil and promotes their decomposition.

The non-condensing gas concentration is preferably at most 1.5 vol %,particularly preferably at most 0.5 vol % by the volume ratio based onthe working fluid, in a gaseous phase of the working fluid.

According to the above-described heat cycle system of the presentinvention, which employs the working fluid of the present invention,practically sufficient heat cycle performance can be obtained whilesuppressing influence over global warming.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to specific Examples. Ex. 1 to 8 and14 to 51 are Examples of the present invention, and Ex. 9 to 13 and 52to 55 are Comparative Examples. Ex. 56 is an Example of R410A (a mixtureof HFC-32 and HFC-125 in a mass ratio of 1:1) used for comparativeevaluation in the following Examples of the present invention andComparative Examples, and is a Reference Example.

Ex. 1 to 13

In Ex. 1 to 13, a working fluid comprising a mixture of HFO-1123 andHFO-1234yf in a proportion as identified in Table 5 was prepared, andthe temperature gradient and the refrigerating cycle performance(refrigerating capacity Q and coefficient of performance COP) weremeasured.

[Measurement of Temperature Gradient and Refrigerating CyclePerformance]

The temperature gradient and the refrigerating cycle performance(refrigerating capacity and coefficient of performance) were measuredwith respect to a case where the working fluid was applied to arefrigerating cycle system 10 as shown in FIG. 2, and a heat cycle asshown in FIG. 4, that is, adiabatic compression by a compressor 11 inthe AB process, isobaric cooling by a condenser 12 in the BC process,isenthalpic expansion by an expansion valve 13 in the CD process andisobaric heating by an evaporator 14 in the DA process, were carriedout.

Measurement was carried out by setting the average evaporationtemperature of the working fluid in the evaporator 14 to be 0° C., theaverage condensing temperature of the working fluid in the condenser 12to be 40° C., the supercooling degree (SC) of the working fluid in thecondenser 12 to be 5° C., and the degree of superheat (SH) of theworking fluid in the evaporator 14 to be 5° C. Further, it was assumedthat there was not loss in the equipment efficiency and no pressure lossin the pipelines and heat exchanger.

The refrigerating capacity and the coefficient of performance wereobtained in accordance with the above formulae (1) and (2) fromenthalpies h in the respective states of the working fluid, i.e. A(after evaporation, high temperature and low pressure), B (aftercompression, high temperature and high pressure), C (after condensation,low temperature and high pressure) and D (after expansion, lowtemperature and low pressure).

The thermodynamic properties required for calculation of the cycleperformance were calculated based on the generalized equation of state(Soave-Redlich-Kwong equation) based on the law of corresponding stateand various thermodynamic equations. If a characteristic value was notavailable, it was calculated employing an estimation technique based ona group contribution method.

The refrigerating capacity and the coefficient of performance wereobtained as relative values based on the refrigerating capacity and thecoefficient of performance of R410A measured in the same manner as abovein the after-mentioned Ex. 56 respectively being 1.000. Further, GWP ofthe working fluid was obtained as the weighted average by thecomposition mass based on the GWPs of the respective compounds shown inTable 4. That is, the sum of products of mass % of the respectivecompounds constituting the working fluid and GWPs was divided by 100 toobtain GWP of the working fluid.

TABLE 4 Compound GWP HFO-1123 0.3 HFO-1234yf 4 HFC-32 675 HFC-134a 1,430HFC-125 3,500 HFO-1234ze(E) 6

The temperature gradient, the refrigerating capacity (relative to R410A)and the coefficient of performance (relative to R410A), and the resultsof calculation of GWP are shown in Table 5.

Further, in FIGS. 5 to 7, graphs respectively illustrating the relationsbetween the composition of the mixed fluid of HFO-1123 and HFO-1234yf,and the temperature gradient, the coefficient of performance (relativeto R410A) and the refrigerating capacity (relative to R410A), are shown.“HFO-1123 [mass %]” indicated by the horizontal axis in FIGS. 5 to 7indicates mass % of HFO-1123 based on the entire amount (100 mass %) ofthe working fluid.

TABLE 5 Relative performance Working fluid composition (relative toR410A) HFO- Co- Temperature HFO-1123 1234yf efficient of Refrigeratinggradient [mass %] [mol %] [mass %] performance capacity [° C.] GWP Ex. 140 48 60 1.002 0.734 8.4 2.5 Ex. 2 50 58 50 0.984 0.805 7.2 2.2 Ex. 3 6068 40 0.966 0.875 5.6 1.8 Ex. 4 70 76 30 0.95 0.945 3.9 1.4 Ex. 5 80 8520 0.938 1.015 2.3 1.0 Ex. 6 85 89 15 0.933 1.05 1.5 0.9 Ex. 7 90 93 100.929 1.083 0.9 0.7 Ex. 8 95 96 5 0.925 1.115 0.4 0.5 Ex. 9 0 0 1001.046 0.422 0.0 4.0 Ex. 10 10 13 90 1.036 0.502 5.4 3.6 Ex. 11 20 26 801.029 0.583 8.0 3.3 Ex. 12 30 37 70 1.018 0.66 9.0 2.9 Ex. 13 100 100 00.921 1.146 0.0 0.3

It is found from the results shown in Table 5 and FIGS. 5 to 7 that theworking fluids in Ex. 1 to 8 having compositions within the range of thepresent invention have favorable coefficient of performance andrefrigerating capacity relative to R410A, and have a predeterminedtemperature gradient or below, as compared with the working fluids inEx. 9 to 13 having compositions out of the range of the presentinvention, having either of the refrigerating capacity and thecoefficient of performance relative to R410A at a low level.

The refrigerating capacity of a working fluid is a factor whichdetermines the size of apparatus itself. If HFO-1123 is combined with acompound having a lower refrigerating capacity than HFO-1123, forexample, HFO-1234yf, the mixture (working fluid) comprising thecombination has a lower refrigerating capacity than the working fluidconsisting solely of HFO-1123. Accordingly, if such a mixture is used asan alternative to R410A, in order to make up for the low refrigeratingcapacity, an increase in the size of an apparatus itself and an increasein the energy used are required.

That is, to combine HFO-1123 and a compound having lower refrigeratingcapacity than HFO-1123 is usually considered to be quite unlikely as ameans to achieve the objects of the present invention. Particularlyunder the present circumstances that replacement of only the workingfluid is desired without replacing a conventional apparatus employingR410A, an increase in the size of the apparatus is unfavorable.

However, for the working fluid of the present invention, HFO-1123 isintentionally combined with HFO-1234yf which is a compound having lowerrefrigerating capacity than HFO-1123, whereby a practically sufficientlevel of the refrigerating capacity was achieved in balance with thefollowing coefficient of performance.

The coefficient of performance of HFO-1123 alone does not reach asufficient level, however, the coefficient of performance of the workingfluid of the present invention comprising a combination of HFO-1123 andHFO-1234yf within the above composition range is favorable. Thecoefficient of performance indicates the efficiency of the working fluidand is very important considering the efficiency of equipment, and is avalue characteristic of the working fluid. Stabilization of thecoefficient of performance within the above range meets the object ofthe present invention such that only the working fluid is replacedwithout changing conventional equipment.

From the viewpoint of the temperature gradient, the temperature gradientcan be suppressed when the content of HEO-1123 is within the range ofthe present invention in combination of HFO-1123 and HFO-1234yf. A toohigh temperature gradient may restrict replacement of R410A. That is,the critical temperature range of the working fluid of the presentinvention is suppressed to be within the same range as that of R410A.

Accordingly, according to the working fluids in Ex. 1 to 8, practicallysufficient cycle performance can be obtained while suppressing influenceover global warming.

Ex. 14 to 39

In Ex. 14 to 39, working fluids comprising a mixture of HFO-1123 andHFO-1234yf, and HFC-134a, HFC-125 or HFC-32 in a proportion asidentified in Table 6, 7 or 8 were prepared. In Tables 6 to 8,1123/(1123+1234yf) [wt %] represents the proportion by mass % ofHFO-1123 based on the total amount of HFO-1123 and HFO-1234yf.

Further, with respect to the obtained working fluids, the temperaturegradient and the refrigerating cycle performance (refrigerating capacityQ and coefficient of performance COP) were measured by the same methodas above. The refrigerating capacity and the coefficient of performancewere obtained as relative values based on the refrigerating capacity andthe coefficient of performance of R410A measured in the same manner asabove in the after-mentioned Ex. 56 respectively being 1.000. Thetemperature gradient, the refrigerating capacity (relative to R410A) andthe coefficient of performance (relative to R410A), and the results ofcalculation of GWP are shown in Tables 6 to 8.

TABLE 6 Relative performance Working fluid composition (relative toR410A) HFO- 1123/(1123 + Coefficient Temperature HFO-1123 1234yfHFC-134a 1234yf) of Refrigerating gradient [mass %] [mol %] [mass %][mass %] [mass %] performance capacity [° C.] GWP Ex. 14 40 48 50 1044.4 1.003 0.742 7.3 145.1 Ex. 15 50 58 40 10 55.6 0.987 0.812 6.3 144.8Ex. 16 60 67 30 10 66.7 0.972 0.880 5.0 144.4 Ex. 17 70 76 20 10 77.80.959 0.947 3.7 144.0 Ex. 18 80 84 10 10 88.9 0.948 1.012 2.5 143.6

TABLE 7 Relative performance Working fluid composition (relative toR410A) HFO- 1123/(1123 + Coefficient Temperature HFO-1123 1234yf HFC-1251234yf) of Refrigerating gradient [mass %] [mol %] [mass %] [mass %][mass %] performance capacity [° C.] GWP Ex. 19 40 48 55 5 42.1 0.9950.751 7.8 177.3 Ex. 20 50 58 45 5 52.6 0.977 0.823 6.5 177.0 Ex. 21 6068 35 5 63.2 0.959 0.893 4.6 176.6 Ex. 22 70 77 25 5 73.7 0.944 0.9643.2 176.2 Ex. 23 80 85 15 5 84.2 0.933 1.034 1.6 175.8 Ex. 24 90 93 5 594.7 0.924 1.101 0.5 175.5

TABLE 8 Relative performance Working fluid composition (relative toR410A) HFO- 1123/(1123 + Coefficient Temperature HFO-1123 1234yf HFC-321234yf) of Refrigerating gradient [mass %] [mol %] [mass %] [mass %][mass %] performance capacity [° C.] GWP Ex. 25 40 44 50 10 44.4 0.9950.820 7.3 69.6 Ex. 26 50 53 40 10 55.6 0.977 0.891 5.9 69.3 Ex. 27 60 6230 10 66.7 0.960 0.962 4.3 68.9 Ex. 28 70 70 20 10 77.8 0.947 1.034 2.668.5 Ex. 29 80 78 10 10 88.9 0.936 1.105 1.1 68.1 Ex. 30 40 40 40 2050.0 0.988 0.900 6.0 136.7 Ex. 31 50 48 30 20 62.5 0.971 0.972 4.5 136.4Ex. 32 60 57 20 20 75.0 0.956 1.045 2.9 136.0 Ex. 33 70 64 10 20 87.50.944 1.118 1.3 135.6 Ex. 34 60 52 10 30 85.7 0.954 1.124 1.5 203.1 Ex.35 55 49 15 30 78.6 0.960 1.086 2.3 203.3 Ex. 36 55 51 20 25 73.3 0.9621.048 3.0 169.7 Ex. 37 50 45 20 30 71.4 0.967 1.049 3.0 203.5 Ex. 38 4037 30 30 57.1 0.983 0.975 4.6 203.8 Ex. 39 30 28 40 30 42.9 0.999 0.9025.8 204.2

It is found from the results shown in Tables 6 to 8 that the workingfluids in Ex. 14 to 33 having compositions within the range of thepresent invention have favorable coefficient of performance andrefrigerating capacity relative to R410A, and a predeterminedtemperature gradient or below.

The working fluids in Ex. 14 to 39 contain HFC-134a, HFC-125 or HFC-32having high GWP as compared with HFO-1123 and HFO-1234yf, however, thecontent is at most 30 mass % based on the entire amount of the workingfluid, and GWP of each working fluid is also within a practical range.

Accordingly, according to the working fluids in Ex. 14 to 39,practically sufficient cycle performance can be obtained whilesuppressing influence over global warming.

Ex. 40 to 52

In Ex. 50 to 52, working fluids comprising HFO-1123, HFO-1234yf andHFO-1234ze(E) in a proportion as identified in Table 9 were prepared.Further, in Ex. 52, a working fluid consisting solely of HFO-1234ze(E)was prepared. In Table 9, 1123/(1123+1234yf) [wt %] represents theproportion by mass % of HFO-1123 based on the total amount of HFO-1123and HFO-1234yf.

Further, with respect to the obtained working fluids, the temperaturegradient and the refrigerating cycle performance (refrigerating capacityQ and coefficient of performance COP) were measured by the same methodas above. The refrigerating capacity and the coefficient of performancewere obtained as relative values based on the refrigerating capacity andthe coefficient of performance of R410A measured in the same manner asabove in the after-mentioned Ex. 56 relatively being 1.000. Thetemperature gradient, and the refrigerating capacity (relative to R410A)and the coefficient of performance (relative to R410A) and the resultsof calculation of GWP are shown in Table 9.

TABLE 9 Relative performance Working fluid composition (relative toR410A) HFO- HFO- 1123/(1123 + Co-efficient Temperature HFO-1123 1234yf1234ze(E) 1234yf) of Refrigerating gradient [mass %] [mol %] [mass %][mass %] [mass %] performance capacity [° C.] GWP Ex. 40 40 48 50 1044.4 1.008 0.724 8.8 2.7 Ex. 41 50 58 40 10 55.6 0.991 0.793 7.8 2.4 Ex.42 60 68 30 10 66.7 0.974 0.861 6.4 2.0 Ex. 43 70 76 20 10 77.8 0.9580.928 4.8 1.6 Ex. 44 80 85 10 10 88.9 0.946 0.995 3.3 1.2 Ex. 45 30 3750 20 37.5 1.028 0.641 9.5 3.3 Ex. 46 40 48 40 20 50.0 1.014 0.712 9.42.9 Ex. 47 50 58 30 20 62.5 0.998 0.780 8.6 2.6 Ex. 48 60 68 20 20 75.00.982 0.845 7.3 2.2 Ex. 49 70 76 10 20 87.5 0.966 0.909 6.0 1.8 Ex. 5050 58 20 30 71.4 1.006 0.764 9.5 2.8 Ex. 51 60 68 10 30 85.7 0.990 0.8278.5 2.4 Ex. 52 0 0 0 100 — 1.084 0.336 0.0 6.0

It is found from the results shown in Table 9 that the working fluids inEx. 40 to 51 having compositions within the range of the presentinvention have favorable coefficient of performance and refrigeratingcapacity relative to R410A, and have a predetermined temperaturegradient or below.

The working fluids in Ex. 40 to 51 contain HFO-1234ze(E) which is veryinferior in the refrigerating capacity as shown in Ex. 52 as comparedwith HFO-1123 and HFO-1234yf, however, its content is at most 30 mass %based on the entire amount of the working fluid, and the refrigeratingcycle performance as the working fluid is within a practical range.

Accordingly, according to the working fluids in Ex. 40 to 51, apractically sufficient cycle performance can be obtained whilesuppressing influence over global warming.

Ex. 53 to 55

Ex. 53 to 55 are Examples of working fluids comprising a combination ofHFO-1123 and HFO-1234ze(E) instead of HFO-1234yf in a proportion asidentified in Table 10, and are Comparative Examples.

With respect to such working fluids, the temperature gradient and therefrigerating cycle performance (refrigerating capacity Q andcoefficient of performance COP) were measured in the same method asabove. The refrigerating capacity and the coefficient of performancewere relative values based on the refrigerating capacity and thecoefficient of performance of R410A measured in the same manner as abovein the after-mentioned Ex. 54 respectively being 1.000. The temperaturegradient, the refrigerating capacity (relative to R410A) and thecoefficient of performance (relative to R410A) and the results ofcalculation of GWP are shown in Table 10.

TABLE 5 Relative performance Working fluid composition (relative toR410A) HFO- Co- Temperature HFO-1123 1234ze(e) efficient Refrigeratinggradient [mass %] [mol %] [mass %] of performance capacity [° C.] GWPEx. 53 40 48 60 1.046 0.655 13 3.7 Ex. 54 50 58 50 1.025 0.732 11.8 3.2Ex. 55 60 68 40 1.000 0.808 9.8 2.6

As shown in Table 10, the working fluids in Ex. 53 to 55 containingHFO-1123 and HFO-1234ze(E) have a great temperature gradient, andalthough influence over global warming can be suppressed, a practicallysufficient cycle performance can hardly be obtained.

Ex. 56

In Ex. 56, with respect to R410A (a mixture of HFC-32 and HFC-125 in amass ratio of 1:1) to be relative comparison with the above Ex. 1 to 55,the temperature gradient and the refrigerating cycle performance(refrigerating capacity Q and coefficient of performance COP) weremeasured in the same manner as the above. The refrigerating capacity andthe coefficient of performance are 1.000 as shown in Table 11. Thetemperature gradient and the result of calculation of GWP are shown inTable 11.

TABLE 11 Relative performance Working (relative to R410A) fluidcomposition Co- Temperature [mass %] efficient of Refrigerating gradientHFC-125 HFC-32 performance capacity [° C.] GWP Ex. 56 50 50 1.000 1.0000.2 2,087.5 (R410A)

Since R410A is a conventional working fluid, the cycle performance isbased on this working fluid in Examples, and when the cycle performanceof a working fluid reaches the same level, the working fluid isevaluated to have practically sufficient cycle performance. R410Aconsists solely of HFC, and has high GWP.

It is found from the above results that in Ex. 1 to 8 and 14 to 51 whichare Examples of the present invention, GWP is low, and based on R410A,the cycle performance is at a practically sufficient level. Further, theworking fluids in Ex. 1 to 3, 14 to 16, 19 to 21, 25 to 28 and 30 to 39are working fluids having a HFO-1123 content of at most 70 mol % andhaving no self-decomposition property, and are working fluids with goodworkability which require no time and effort for securing the safety.

[Estimation of Critical Temperature]

With respect to HFO-1123, HFO-1234yf and a mixed fluid of them having acomposition as identified in Table 12, the critical temperature wasestimated by visually observing the position of extinction of thegas-liquid interface and coloring by critical opalescence. The resultsare shown in Table 12 and FIG. 8. “HFO-1123 [wt %]” indicated by thehorizontal axis in FIG. 8 indicates mass % of HFO-1123 based on theentire amount (100 mass %) of the mixed fluid.

TABLE 12 Composition of mixed fluid [mass %] HFO-1123 HFO-1234yfCritical temperature [° C.] 0 100 94.7 50 50 76.9 70 30 69.9 100 0 59.2

As shown in FIG. 8, the critical temperature increases by combination ofHFO-1123 and HFO-1234yf as compared with HFO-1123 alone. That is, themixed fluid of HFO-1123 and HFO-1234yf may have a higher criticaltemperature as compared with a critical temperature of HFO-1123 alone of59.2° C. It is found from FIG. 8 that when the proportion of HFO-1234yfis at least 5 mass % based on the total amount of HFO-1234yf andHFO-1123, a sufficient critical temperature as an alternative to R410Ais obtained. Accordingly, by combination of HFO-1123 and HFO-1234yf, aworking fluid which is widely applicable as an alternative to R410A canbe provided.

HFO-1234yf has a lower refrigerating capacity than HFO-1123. However,the present inventor has found that by the mixture ratio within theabove range, a decrease in the capacity by mixing of HFO-1234yf can bemade up for by a conventional technique, and accomplished the presentinvention. The present invention is useful under the presentcircumstances such that only replacement of the R410A working fluid isdesired without replacement of equipment as described above.

INDUSTRIAL APPLICABILITY

The working fluid of the present invention is useful as a refrigerantfor a refrigerator (such as a built-in showcase, a separate showcase, anindustrial fridge freezer, a vending machine or an ice making machine),a refrigerant for an air-conditioning apparatus (such as a roomair-conditioner, a store package air-conditioner, a building packageair-conditioner, a plant package air-conditioner, a gas engine heatpump, a train air-conditioning system or an automobile air-conditioningsystem), a working fluid for power generation system (such as exhaustheat recovery power generation), a working fluid for a heat transportapparatus (such as a heat pipe) or a secondary cooling fluid.

This application is a continuation of PCT Application No.PCT/JP2014/068084 filed on Jul. 7, 2014, which is based upon and claimsthe benefit of priority from Japanese Patent Application No. 2013-146298filed on Jul. 12, 2013 and Japanese Patent Application No. 2014-017030filed on Jan. 31, 2014. The contents of those applications areincorporated herein by reference in their entireties.

REFERENCE SYMBOLS

-   10: refrigerating cycle system, 11: compressor, 12: condenser, 13:    expansion valve, 14: evaporator, 15, 16: pump.

1-15. (canceled)
 16. A working fluid for heat cycle, comprising:trifluoroethylene, 2,3,3,3-tetrafluoropropene, and optionally ahydrofluoroolefin other than trifluoroethylene and2,3,3,3-tetrafluoropropene, wherein a total proportion oftrifluoroethylene and 2,3,3,3-tetrafluoropropene based on an entireamount of the working fluid is from 70 to 100 mass %.
 17. The workingfluid according to claim 16, comprising the hydrofluoroolefin other thantrifluoroethylene and 2,3,3,3-tetrafluoropropene, which is ahydrofluorocarbon containing a carbon-carbon double bond.
 18. Theworking fluid according to claim 17, wherein the hydrofluorocarboncontaining a carbon-carbon double bond is at least one selected from thegroup consisting of 1,2-difluoroethylene, 2-fluoropropene,1,1,2-trifluoropropene, trans-1,2,3,3,3-pentafluoropropene,cis-1,2,3,3,3-pentafluoropropene, trans-1,3,3,3-tetrafluoropropene,cis-1,3,3,3-tetrafluoropropene, and 3,3,3-trifluoropropene.
 19. Theworking fluid according to claim 16, further comprising a saturatedhydrofluorocarbon.
 20. The working fluid according to claim 19, whereinthe saturated hydrofluorocarbon is at least one selected from the groupconsisting of difluoromethane, 1,1-difluoroethane,1,1,1-trifluoroethane, 1,1,2,2-tetrafluoro ethane,1,1,1,2-tetrafluoroethane, and pentafluoroethane.
 21. A composition fora heat cycle system, comprising: the working fluid according to claim 16and a lubricating oil.
 22. A heat cycle system, comprising thecomposition according to claim
 21. 23. The heat cycle system accordingto claim 22, which is a refrigerating apparatus, an air-conditioningapparatus, a power generation system, a heat transport apparatus or asecondary cooling machine.
 24. The heat cycle system according to claim22, which is a room air-conditioner, a store package air-conditioner, abuilding package air-conditioner, a plant package air-conditioner, a gasengine heat pump, a train air-conditioning system, an automobileair-conditioning system, a built-in showcase, a separate showcase, anindustrial fridge freezer, an ice making machine or a vending machine.